It is well known to utilize a positron emission tomography (PET) camera for measuring the concentrations of positron emitting radioisotopes inserted into a patient. Electromagnetic radiation is emitted in the form of two gamma rays of equal energy (511 keV), which are emitted 180.degree. to each other. A count of this annihilation radiation is detected externally and is used to measure both the quantity and the location of the positron emitter.
One problem of the PET camera is that it measures, in addition to the true counts, background noise which includes random or accidental and scattered coincidences. These random counts and scatter counts constitute a significant portion of the total counts measured by the PET camera.
Another problem is that the current PET cameras are very expensive with the camera itself costing more than one million dollars and a cyclotron to produce radioisotopes costs two million dollars. The only PET blood flow radionuclear tracer which does not need the cyclotron is rubidium-82 (Rb-82). Using Rb-82, the PET technology can be potentially afforded if the cost of the PET camera can be lowered. However, Rb-82 has a short 66 seconds half life and the total counts collected are rather low even though the initial counts are high enough to saturate most cameras. To produce a good Rb-82 image, the primary requirement for the camera is the ability to transfer or process data at extremely high data rates to accomodate the very high initial Rb-82 activity. The required data processing capability is very expensive. This is especially the case if the first pass injection bolus is to be measured. No existing camera can measure this bolus input function without injecting a much lower dosage, which in turn sacrifices the later phase tissue uptake image.
Since the maximum PET camera data transfer capability is limited, it is conventional to inject only the maximum radioisotope activity into the patient which can be processed by the maximum transfer rate of the camera without saturation and the data collection continues until the activity/data rate is insignificantly low, which in the case of Rb-82 is typically about 3 minutes which lowers the statistical quality of the latter phase image.
The present method and apparatus is directed to providing a new PET data collection method which can improve image quality by approximately doubling the true counts and allows the PET camera to handle a larger dynamic range, for example, 4 or 5 times, of activity without saturation and without increasing the data processing capability of the PET camera, which is extremely expensive. And presently the camera sensitivity is already near the theoretical limit. Therefore, the present method appears to be the only viable way of increasing the detected true counts.